1. Field of the Invention:
The present invention relates to a process for the preparation of aldehydes by hydroformylation of olefins, and, more especially, relates to such hydroformylation of olefins in the presence of a rhodium containing, aqueous solution of certain sulfonated aryl phosphine compounds.
2. Description of the Prior Art:
It is well known in the art to produce aldehydes by hydroformylation, by reacting an olefin with carbon monoxide and hydrogen, said process being carried out in an organic liquid medium which contains, as catalyst, a compound based on a metal of Group VIII of the periodic classification or table of elements [compare Handbook of Chemistry and Physics, 53rd edition], and especially which contains a soluble complex formed from one of the above metal compounds and at least one organic ligand which has, in its molecule, an atom of an element of Group VA of the periodic classification, such as tertiary arsines, tertiary stibines or tertiary phosphines.
Among the catalyst systems to date envisaged, those complexes resulting from the reaction of an inorganic or organic derivative of rhodium with an excess of tertiary phosphine, tertiary arsine or tertiary stibine, such as triphenylphosphine, triphenylarsine or triphenylstibine, appear the most attractive. In general, these reactions are carried out in a solvent such as an aromatic hydrocarbon [benzene or toluene], a saturated cycloaliphatic hydrocarbon [cyclopentane or cyclohexane], an ether [diisopropyl ether, dibutyl ether of ethylene glycol], a ketone [acetone or methylethyl ketone], an aliphatic or cycloaliphatic alcohol [methanol, ethanol, butanol, hexanol or cyclohexanol], an ester such as those derived from alkylcarboxylic or arylcarboxylic acids and aliphatic or cycloaliphatic alcohols [ethyl acetate, cyclohexyl acetate, diethyl oxalate or methyl benzoate], or lactones [butyrolactone or valerolactone] [compare, in particular, U.S. Pat. Nos. 3,511,880 and 3,801,646 and French Pat. No. 1,560,961].
Under these conditions, resorting to these complexes based on rhodium and a ligand containing trivalent phosphorus, arsenic or antimony atoms renders it possible to conduct the hydroformylation with very small amounts of the noble metal, and at a low pressure. It should further be noted that the concomitant hydrogenation of the aldehydes is extremely slight and that, consequently, the desired aldehydes are the principal products. The hydrogenation of the reactant olefin is also very slight. In the majority of cases, use of these catalyst systems makes it possible to direct the hydroformylation of linear olefins, having a terminal or internal double bond, towards the predominant formation of aldehydes having a linear chain or a short side chain, so that the selectivity of the reaction in this respect, measured by the percentage of linear isomers or of isomers having a short side chain, contained in the aldehyde resultant products, is generally greater than 50%. Thus, this selectivity can be as much as 90%, and even in excess of this value. In the case of the lower linear olefins, such as propylene, it is however to be noted that the achievement of high selectivities in respect of aldehydes having a linear chain requires considerable expenditure on ligands based on phosphorus [triphenylphosphine], on arsenic [triphenylarsine] or on antimony [triphenylstibine], because under these conditions such ligands are themselves used as the reaction medium, in the absence of any other organic solvent [compare French Pat. No. 2,072,146 and British Pat. No. 1,357,735].
Ultimately, the striking catalytic properties of the aforementioned soluble complexes based on rhodium have enriched the state of the art by providing an easily performed method for the preparation of aldehydes. However, a notable disadvantage of those liquid phase hydroformylation processes above described, in which the catalyst systems employed are homogeneous and in solution, resides in the fact that they require a difficult supplementary treatment for the purpose of separating the hyroformylation products from the catalyst solution, and the catalyst is only difficultly recovered in order to recycle same to the reaction zone; for example, the catalyst can be recycled in the non-volatile residue obtained after distillation of the oxygen-containing reaction products. In fact, such a treatment of the catalyst solution can only be validly applied to processes for the hydroformylation of lower olefins which provide volatile reaction products. Furthermore, it has also been found that this treatment gives rise to substantial loss of catalyst; the catalyst solutions decompose readily during the treatment stages so that the noble metal is lost by precipitation of its metallic form. The presence of catalyst in the reaction products after they have been separated is also observed. The residual catalyst system thus loses its efficiency, which reduces the industrial value of such hydroformylation processes.
In order to overcome these disadvantages and reduce the losses of rhodium, it has also been proposed to use a heterogeneous solid catalyst which can easily be separated from the reaction medium, for example, by fixing the rhodium complex on a porous solid support [compare French Pat. No. 2,069,322] or by combining a rhodium derivative with a polymer [polystyrene or polyvinyl chloride] containing a phosphine [compare French Pat. No. 2,047,476]. However, the solid phase catalysts possess certain disadvantages, and, in particular, there has been observed a limitation on the selectivity of the catalyst system with regard to the formation of aldehydes having a linear chain or a short side chain, from linear olefins having a terminal or internal double bond.
A need thus exists to provide a process for the hydroformylation of olefins, in liquid phase, in the presence of a catalyst based on rhodium, which obviates the disadvantages of the prior processes relating to the recovery of the catalyst, while at the same time preserving the aforementioned advantages, especially the high yields of aldehyde products and the excellent selectivities in respect of aldehydes having a linear chain or a short side chain.